EP1486465A1 - Process for biological treatment of effluents - Google Patents

Abstract

A method of treating polluted effluents such as domestic and industrial waste water comprising at least one stage of biological treatment leading to the formation of sludge mixtures comprising organic sludges and water which comprises a stage of control of bacterial growth in at least part of the sludge mixtures and at least part of the raw effluents. The method comprises a stage of aerobic treatment of the effluent, a clarification stage, which may be replaced by a membrane filtration stage, and a thickening stage. It may further comprise stages of (1) anaerobic treatment; (2) a second aerobic treatment. The outputs of any or all of these stages may be fed to the control stage or recycled upstream of it into the raw effluent. Control of bacterial growth is achieved by regulating the oxido-reduction potential of the sludge mixture. The potential is regulated to between -50mV and +50mV and more preferably -20mV to +20mV with respect to a normal hydrogen electrode. The potential is measured by use of a platinum or gold measurement electrode and a Ag/AgCl or Hg/HgCl 2 (calomel) reference electrode. The measurement system is connected to an automatic control system. Regulation of the potential is achieved by (1) regulation of the feed of raw effluents into the bacterial growth control basin; (2) regulation of the flow of sludge mixtures into the control basin; (3) regulation of the evacuation of liquor from the control basin to an aerobic or anaerobic basin; (4) aeration of the basin with air or oxygen. The bacterial growth control stage may further comprise (1) the addition of reagents such as sodium hydroxide, acid or oxidant; (2) the injection of steam; (3) raising the temperature of the medium; (4) application of mechanical shear.

Description

The present invention relates to a treatment method biological effluents polluted for their purification, such as in particular, but not exclusively, industrial wastewater and urban.

In conventional biological treatments, used for example in liquid effluent treatment plants, these effluents with biomass (bacteria). The implementation of some biological process requires oxygen (air oxygen and / or pure oxygen) for the oxidation of carbon pollution and the nitrification of nitrogen pollution. In contrast, other biological processes performed in the absence of oxygen (anoxic zone for denitrification and anaerobic zone for phosphorus removal) such as those used for the removal of nitrites, nitrates and partially phosphorus. Bacteria get the energy they need to survive and get reproduce in organic matter contained in waters waste. Thus the purification is ensured by the action of bacteria on the organic matter transforming the latter into carbon dioxide, nitrogen and water.

Although such processes ensure good water purification, they do however lead to a gradual increase in the amount of biomass forming very organic sludge which is generally required concentrate by thickening and dehydration before eliminating them by agricultural spreading by composting, landfill or incineration.

Industrial and urban wastewater increasing without ceases, the quantity of organic sludge generated by the treatment is more and more important and poses a real problem as for their recycling. Indeed, the aforementioned recycling methods require the implementation of complex and costly means.

To date, many proposals aim to improve the treatment processes so that they generate less sludge residual. One proposal is to partially hydrolyze the sludge, that is to say destroying part of the microorganisms that make up sludge by making it partially soluble. Products from hydrolysis that contain soluble organic compounds can then be sent back to the top of the biological treatment, during which the microorganisms will treat hydrolyzed microorganisms. A common technique is to perform basic or acid hydrolysis to using chemical agents possibly coupled with an elevation of temperature. However, this hydrolysis technique requires the readjustment of the pH and temperature of the solution before reinjection in the biological tank (s). Another drawback of this type hydrolysis is to increase the salinity of hydrolyzed sludge which can lead to dysfunction of the biological treatment stage. Certain processes, in particular those described in document US-A-4,915,840, implement an additional digestion step biological of part of the organic matter. This digestion, which addition must be carried out under conditions of determined temperature, complicates the entire processing device.

Another solution to remove sludge during treatment effluent consists of installing a grinder in the recirculation loop mixed liquor from the biological treatment tank (s). This makes it possible to cause part of the cells to burst bacteria constituting said sludge. The technology used, such as by example, that a mechanical grinding, a compression / expansion grinding or by sonochemistry, causes part of the cells to burst bacteria constituting said sludge. This technique is generally simple to implement but has the drawback of only reducing weakly producing excess sludge.

Other proposals are based on the action of oxidizing agents on muddy mixtures recycled in an organic tank in order to reduce the production of excess sludge. The process described in the patent application US-A-5,858,222 thus proposes to act on ozone on the muddy mixture which includes organic mud particles and some water. The main disadvantage of ozone is the inherent difficulties the very use of this highly oxidizing reagent and its cost. other oxidants such as air, hydrogen peroxide or oxygen under pressure can be used conventionally or in methods wet oxidation (OVH, in English "Wet Air Oxidation") such as described, for example, in document FR-A- 2,774,980, are not fairly effective alone: they must be combined with heating, pH adjustment and / or catalyst, which complicates and increases also the cost of these processes.

The present invention relates to an improvement of biological effluent treatment processes to reduce or even eliminate the quantity of excess sludge produced by them, and which does not present not the disadvantages of the aforementioned prior techniques.

To this end, the invention provides a method for treating effluents. crude polluted, such as industrial and urban waste water, comprising at least one step of biological treatment of effluents crudes leading to the production of muddy mixtures with organic sludge and water, characterized in that it also includes a step of controlling the bacterial growth of at least part muddy mixtures and at least some of the raw effluents to be treated. This control step is to prevent the development and bacterial growth in the control basin by inhibition of biological growth processes. The control step is carried out in at least one receiving basin for the part of the muddy mixtures and the part of the raw effluents to be treated.

• une étape de traitement biologique aérobie des effluents bruts dans au moins un bassin aéré,
• et une étape de clarification des mélanges boueux dans au moins un clarificateur.

In an implementation variant, the method comprises:

• a step of aerobic biological treatment of the raw effluents in at least one aerated basin,
• and a step of clarifying the muddy mixtures in at least one clarifier.

The method can also optionally include a step thickening the sludge in at least one thickener.

The muddy mixtures are taken from at least one of the above three steps to be subjected to growth control bacterial.

In another variant, the biological treatment method includes an additional step of biological treatment of effluents raw in at least one unventilated tank. Muddy mixtures are taken from at least this additional step or one of three aforementioned stages (biological treatment in aerated tank (s), clarification, thickening) to be controlled for bacterial growth.

In another variant, the biological treatment method includes a second step of aerobic biological treatment of raw effluents in at least one aerated tank. Muddy mixtures can then be taken from at least this other stage or one of the 4 aforementioned steps (biological treatment in aerated tank (s), treatment organic in non-aerated tank (s), clarification, thickening) to be subject to bacterial growth control.

In another variant, the clarification step is replaced by a membrane filtration step of the muddy mixtures produced by the stages of biological treatments. Muddy mixtures subjected to the stage bacterial growth control can also be taken since this filtration step.

According to particular features of the invention, at least one part of the muddy mixtures can be introduced directly into the basin for bacterial growth or can be recycled upstream of the control tank for bacterial growth in raw effluents.

An interesting feature of the invention is that the growth of the muddy mixture contained in the basin of the stage of control is controlled by measuring and regulating the redox potential of this muddy mixture. The redox potential of muddy mixture contained in the control stage basin is regulated around a redox potential value close to zero corresponding to the balance between oxidizing medium and reducing medium in the muddy mixture. During the control of bacterial growth, the redox potential of the muddy mixture is regulated to be maintained between a negative value equal to approximately - 50mV compared to the normal hydrogen electrode and a positive value equal to about + 50mV compared to the normal hydrogen electrode. The redox potential muddy mixture can also be regulated to be maintained between a negative value equal to approximately - 20mV compared to the normal hydrogen electrode and a positive value equal to about + 20mV compared to the normal hydrogen electrode.

In another variant, the redox potential of the mixture muddy is regulated around a predetermined potential value and between - 150 mV and + 150 mV compared to the normal electrode at hydrogen. During the control of bacterial growth, the potential redox of the muddy mixture is regulated to be maintained in an interval which is approximately plus or minus 50 mV from the value of predetermined potential, the difference of 50 mV being expressed as a function of the normal hydrogen electrode. The redox potential of muddy mixture can also be regulated to be kept in a interval which is approximately plus or minus 20 mV from the value of predetermined potential, the difference of 20 mV being expressed as a function the normal hydrogen electrode.

The measurement of the value of the redox potential is obtained from measuring means comprising at least one measuring electrode made of platinum or gold and a reference electrode Ag / AgCl or Hg / HgCl ₂ (calomel electrode) . The measurement means can be a measurement sensor cooperating with an automaton which regulates the redox potential. The regulation of the redox potential can be obtained by controlling the supply of the raw effluents to be treated, for example by regulating the supply rate of these effluents, entering directly into the bacterial growth control basin. Regulation of the redox potential can also be obtained by controlling the evacuation of the liquor from the control tank to at least one aerated tank or at least one non-ventilated tank. This control can consist of a regulation of the rate of evacuation of the liquor from the control basin to at least one aerated basin or at least one non-aerated basin. Another possibility is to regulate the redox potential by sequencing aeration with air or pure oxygen from the control tank. In an alternative implementation of a method according to the invention, the regulation of the redox potential is carried out by controlling the supply of muddy mixtures recycled into the control tank from at least one aerated tank, at least one non-aerated basin, at least one clarifier and / or at least one thickener.

Another characteristic of the invention is that the circulation of effluents between at least two stages of biological treatment and / or between the control step and at least one biological treatment step can be performed in one direction or opposite.

• une addition de réactifs tels par exemple que de la soude, un acide ou un oxydant,
• une injection de vapeur,
• une augmentation de la température du milieu,
• un cisaillement mécanique du mélange boueux, par exemple, par une turbine à grande vitesse ou par un hydro-éjecteur.

In another variant implementation of the method, the control step comprises:

• an addition of reagents such as, for example, sodium hydroxide, an acid or an oxidant,
• steam injection,
• an increase in the temperature of the medium,
• mechanical shearing of the muddy mixture, for example, by a high speed turbine or by a hydro-ejector.

According to an interesting characteristic of the invantion, the step of control can be carried out in at least one buffer tank of a treatment facility.

• la figure 1 est un organigramme représentant un premier mode de mise en oeuvre du procédé de traitement d'effluents selon l'invention ;
• la figure 2 est un organigramme représentant un autre mode de mise en oeuvre du procédé selon l'invention ;
• la figure 3 est un organigramme représentant un troisième mode de mise en oeuvre du procédé selon l'invention ;
• la figure 4 est un organigramme représentant un quatrième mode de mise en oeuvre du procédé l'invention ;
• la figure 5 est un organigramme représentant un cinquième mode de mise en oeuvre du procédé l'invention.

The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading the description which follows, given by way of example with reference to the appended drawings, in which:

• Figure 1 is a flowchart showing a first embodiment of the effluent treatment method according to the invention;
• FIG. 2 is a flowchart showing another mode of implementation of the method according to the invention;
• Figure 3 is a flowchart showing a third embodiment of the method according to the invention;
• Figure 4 is a flowchart showing a fourth embodiment of the method of the invention;
• Figure 5 is a flowchart showing a fifth embodiment of the method of the invention.

The method of FIG. 1, which can be implemented in a industrial and urban wastewater treatment plant 1, can understand five processing steps: a pretreatment step 3 of crude effluent 2 which is not always required, an aerobic stage of biological treatment 4 in several aerated basins (referenced 4 ') generating a muddy mixture comprising organic sludge and water, a clarification step 5 of the muddy mixture in several clarifiers (also referenced 5 '), a thickening step 6 of sludge in a thickener (referenced 6 ') and a control step 7 of the bacterial growth in a control basin (referenced 7 ').

The pretreatment step 3 consists in eliminating, if necessary, bulky materials for example by screening or sieving, remove sands and grease for example using a degreaser, oil separator or sand separator, or to remove materials in suspension or hydrocarbons for example by decantation primary or by flotation. The raw effluents that can be taken at the outlet of this step 3 usually have a negative redox potential like the raw effluents 2 which can be taken directly from a collection pit (not shown) for polluted raw effluents.

The aerobic biological treatment step 4 consists in contact the effluents to be treated 2 with a biomass in the presence of oxygen (air oxygen and / or pure oxygen) for the oxidation of pollution carbonaceous and nitrogenous. It is also possible, in such a step 4, to treat phosphorus by biological assimilation. Treatment basins aerobic biological 4 '(and / or 9' Figures 3 and 5) are continuously aerated or sequentially. This step generates a muddy mixture which is composed very organic sludge and water. The sludge collected from these aerated biological treatment tanks 4 '(and / or 9' see Figures 3 and 5) have a positive redox potential while sludge collected from 8 'non-aerated biological treatment tanks, such as those shown in Figures 2 to 5, have a lower redox potential even negative.

Clarification step 5 is used to separate water from solid matter (mud particles) suspended in the muddy mixtures generated by the 4 'aerated basins (and / or 9' see Figures 3 and 5) for biological treatment (and / or not ventilated 8 'Figures 2 to 5). The sludge taken from the 5 'clarifiers have a slightly positive redox potential.

The thickening step 6 ensures the sludge concentration of the muddy mixtures obtained after clarification 5. Sludge collected from the thickener 6 'have a negative or even very redox potential negative.

• E_o Ag/AgCl / EHN est la valeur du potentiel d'oxydo-réduction préalablement déterminée par rapport à celui de l'électrode normale à hydrogène,
• E Ag/AgCl est la valeur du potentiel d'oxydo-réduction du mélange boueux directement mesurée dans le bassin de contrôle 7' et déterminée à l'aide de l'électrode de mesure en platine et de électrode de référence Ag/AgCl,
• E Ag/AgCl / EHN est la valeur du potentiel d'oxydo-réduction du mélange boueux contenu dans le bassin de contrôle 7' déterminée par rapport à l'électrode normale à hydrogène.

The control step 7 consists in subjecting to a control of the bacterial growth, the raw effluents 2 to be treated and the muddy mixtures coming from the biological treatment steps 4 (8 or 9 FIGS. 2 to 5) and from the step of 6 thickening of sludge, to limit or prevent the development of biomass. The control of bacterial growth in the control tank 7 ′ can be continuous or triggered in cycles as a function, for example, of a minimum quantity of sludge stored in the control tank 7 ′. When controlling bacterial growth, the redox potential of the mixture contained in the control tank 7 ', which may vary depending on the supply of muddy effluents and / or crude effluents 2, is precisely evaluated and continuously by measurements which are carried out from a platinum (or gold) measurement electrode and an Ag / AgCl (or Hg / HgCl ₂ ) reference electrode immersed directly in the control tank 7 'or placed in a bypass line. The measurements are then corrected to obtain the value of the redox potential of the muddy mixture contained in the control tank 7 'relative to the normal hydrogen electrode (EHN) according to the formula: E Ag / AgCl / EHN = E Ag / AgCl + E _o Ag / AgCl / EHN. In this formula:

• E _o Ag / AgCl / EHN is the value of the redox potential previously determined relative to that of the normal hydrogen electrode,
• E Ag / AgCl is the value of the redox potential of the muddy mixture directly measured in the control tank 7 ′ and determined using the platinum measurement electrode and the Ag / AgCl reference electrode,
• E Ag / AgCl / EHN is the value of the redox potential of the muddy mixture contained in the control tank 7 'determined relative to the normal hydrogen electrode.

According to the results given by the measurements of the values of redox potential, the redox potential of the mixture muddy contained in the control tank 7 'is regulated to obtain a biological balance at the limit between reducing and oxidizing medium. Those are rapid and frequent alternations of the potential between oxidizing medium and reducing medium which then make it possible to conserve a value of the potential redox of the muddy mixture close to the equilibrium value of redox potential (near redox potential value 0 volts) which corresponds to the limit between oxidizing medium and reducing medium. The value of the redox potential of the muddy mixture changes in a closed interval around the equilibrium value. The lower value of this interval is negative and the upper value is positive. When the value of the potential measured in the muddy mixture is close to the value lower or higher interval, the potential is regulated so that its value approaches the equilibrium value. Typically, the interval is delimited by a value less than approximately -20 mV (millivolt) by compared to the normal hydrogen electrode and a higher value equal to about + 20mV compared to the normal hydrogen electrode.

This regulation of the redox potential around and close to the equilibrium value between oxidizing medium and reducing medium is carried out to obtain redox reactions in the 7 'control basin which involve all the oxidizing compounds and compounds reducers. This preserves a physiological imbalance of the biomass leading to significant energy losses (adenosine triphosphate / adenosine diphosphate) and cause degradation of intracellular compounds effectively. In this way and although the 7 'control tank is always supplied with a muddy mixture comprising bacteria and from 4 'biological treatment tanks (8' and / or 9 'Figures 2 to 5), the development and bacterial growth in the control basin 7 'is limited or even blocked and the development of the biomass in the control basin 7 'is also limited or even blocked. he it is also possible to reduce the quantity of biomass in this 7 'basin, therefore limit or prevent the production of sludge biological by the treatment method according to the invention.

In this mode of implementation, the regulation of the potential redox of the muddy mixture in the 7 'control tank and the fast and frequent alternations of this potential around the value balance, are achieved by controlling the quantity of raw effluents 2 supplying the control tank 7 ′ for bacterial growth, the raw effluents 2 making it possible to reduce the redox potential. This control of the quantity of raw effluents 2 supplying the basin 7 'can be obtained by varying the feed rate 10 or by feeding 10 discontinuous raw effluents 2 entering the control tank 7 '.

The regulation of the redox potential is also performed by the recycling control 16 of the liquor from the control basin 7 'to the biological treatment tanks 4' which are then supplied with continuous or sequentially. The recycling 16 of the liquor from the control 7 'to the biological treatment tanks 4' cooperating with the recycling 21 of the fluids taken from these treatment basins biological 4 'to the control basin 7' increases the potential redox in the 7 'control tank.

During general operation of a treatment plant 1 according to the mode of implementation of the process represented in FIG. 1, the effluents rough 2 undergo first, and when required, step 3. The raw pretreated effluents are then sent to the 4 'aerated basins and towards the 7' growth control basin bacterial. After having undergone a biological oxidation treatment in the 4 'aerated tanks, muddy mixtures are sent to the clarifiers 5 '. After being clarified, the purified water is evacuated (circulation 12) from station 1 and the residual sludge from the clarifiers 5 'are evacuated (circulation 14) to the thickener 6 'where they are concentrated. The concentrated sludge is then recycled (circulation 15) to the 7 'control tank where they undergo, with some of the raw effluents 2 pretreated or not pretreated and part of the sludge from the biological treatment 4 control of bacterial growth. The oxidation-reduction potential control degrades the material organic component of the sludge. The liquor from the 7 'control basin as well obtained, which is recycled (circulation 16) to aerated basins 4, contains mainly biodegradable compounds, such as carbon and nitrogen, which are removed and transformed by oxidation and nitrification in aerated basins 4.

Small amounts of sludge, which cannot be removed by the process, undergo, after the thickening step 6, a step of dehydration 24 before being evacuated (evacuation 25) and treated with conventional recycling methods (not shown in the figures).

The increase in recycling rates 21 of sludge since the biological treatment towards the 7 'control basin and the increase in recycling flows 16 from the 7 'control basin to the biological treatments increase the processing load (quantity of sludge per unit of time subjected to control step 7) of control step 7 to improve the effluent treatment capacity crude by the process according to the invention shown in Figure 1 while preserving devices, for example, for thickening 6 of weak capabilities. When control of bacterial growth 7 is interrupted or when the flows of the raw effluents 2 to be treated and muddy mixtures to undergo control step 7 are weak, the recycling 16 and recycling 21 are interrupted and the fluids circulate, between the control tank 7 'and the biological treatment tanks 4', only from the 7 'control tank to the treatment tanks biological 4 '(circulation referenced 20).

To guarantee an effective biological treatment, the concentration sludge in 4 'biological treatment tanks (8' and / or 9 'figures 1 to 5) should be kept at an optimal value. Muddy mixtures waste from the 5 'clarifiers can therefore be recycled (circulation 17), according to a controlled flow or by a sequenced supply, to at least one of the 4 'biological treatment basins (and / or to minus one of the 8 'and / or 9' tanks, see figures 2 to 5) to check the concentration of sludge in this or these basins. The amount of sludge recycled (circulation 17) to the 4 ', 8' and 9 'biological treatment tanks is, for example, increased to adjust the sludge concentration when it is too low.

• uniquement des bassins de traitement biologiques 4'( 8' et/ou 9' figures 1 à 5) et des clarificateurs 5',
• uniquement des clarificateurs 5' si les boues décantées dans les clarificateurs 5' sont toutes recyclées 19 directement dans le bassin de contrôle 7',
• de l'épaississeur 6', des bassins de traitement biologiques 4'( 8' et/ou 9' figures 1 à 5) et des clarificateurs 5' lorsque les boues résiduaires emmagasinées dans les clarificateurs 5' ne sont que partiellement recyclées vers le bassin de contrôle 7'.

The muddy mixtures can also be recycled (circulation 19) from the clarifiers 5 'directly to the control basin 7' to feed (supply 19) the latter with fresh sludge. These partly decanted sludge has a positive redox potential which makes it possible to increase the biological activity of the muddy mixture in the control tank 7 '. The control basin 7 ′ is then fed (feed 10) by the raw effluents 2 pretreated leaving the pretreatment step 3 or not pretreated and coming directly from the pit for raising the raw effluents 2 and by the muddy mixtures coming from either:

• only 4 'biological treatment tanks (8' and / or 9 'Figures 1 to 5) and 5' clarifiers,
• only 5 'clarifiers if the sludge decanted in the 5' clarifiers are all recycled 19 directly into the control tank 7 ',
• thickener 6 ', biological treatment tanks 4' (8 'and / or 9' Figures 1 to 5) and clarifiers 5 'when the residual sludge stored in the clarifiers 5' is only partially recycled to the basin 7 'control.

In an alternative embodiment shown in FIG. 2, a step 8 of biological treatment in the absence of oxygen implemented in non-aerated basins (referenced 8 '), has been added for dephosphating and denitrification of effluents (elimination of nitrites, nitrates and partially phosphorus), dephosphating being obtained by anaerobic biological treatment and denitrification being then obtained by an anoxic biological treatment. This step 8 of Anaerobic and anoxic biological treatments are implemented between the control step 7 and the aerobic step 4 of biological treatment. The raw effluents 2, which have possibly undergone the pretreatment step 3, supply (supply 10) the control basin 7 'and supply, in function of the nitrogen concentrations to be denitrified and phosphorus to be treated present in raw effluents, non aerated 8 'and / or aerated 4' tanks. For example, in the case of a high concentration of nitrogen to be denitrified and in phosphorus to be treated, the raw effluents 2 only supply the 8 'non-aerated basins, the aerated 4' basins then being supplied (circulation 23) by effluents that have already undergone the biological treatment step anaerobic and anoxic 8. Muddy mixtures subject to the control of Bacterial growth 7 come from the biological treatment stage anaerobic and anoxic 8 (circulation 21), from the clarification stage 5 (circulation 19) and / or thickening step 6 (circulation 15). step 7 also eliminating the nitrates contained in the muddy mixtures generates a liquor, rich in compounds biodegradable and free from nitrates. According to traffic 16 this liquor is returned, depending on the nitrogen and phosphorus to be treated present in the liquor of the 7 'control tank, towards the 4 'aerated tanks and / or to the 8' non-aerated treatment tanks organic. For example, if the phosphorus concentrations are high, the liquor from the control tank 7 'is returned only to the 8 'unventilated basins. Conversely, if the phosphorus concentrations are very weak, the liquor is returned only to the aerated basins 4 '. Biodegradable compounds, such as carbon and nitrogen, are then eliminated and transformed by oxidation and nitrification in these aerated basins 4 'and / or by denitrification and phosphate removal in non-aerated basins 8 '.

The increase in recycling rates 22, 21 of aerated basins 4 'to non-aerated basins 8' then 8 'non-aerated basins to control basin 7 'and the increase in recycling rates 16 of control tank 7 'to biological treatment tanks 4', 8 ' allow to increase the processing load of control step 7 (quantity of sludge per unit of time subject to control step 7) to improve the raw effluent treatment capacity 2 of process 1 according to the invention shown in Figure 2. Recycling 22 of aerated basins 4 'to unventilated basins 8' is also necessary to allow to denitrify the nitrogen contained in the 8 'non-aerated basins effluent that was nitrified during aerobic biological treatment step 4. Circulation from non-aerated basins 8 'to aerated basins 4' east necessary to treat in ventilated basins 4 ', not only carbon and nitrogen pollution that have not been oxidized, but also the phosphorus by biological assimilation, when this is in concentration high in raw effluents 2 and when nitrate concentrations are weak.

The muddy mixtures generated by the 5 'clarifiers can be recycled (circulation 14) to the thickener 6 'where the sludge will be concentrated, towards the 7 'control basin to feed (circulation 19) this one with sludge whose biological activity is important and whose redox potential is positive, towards the 4 'aerated basins and / or 8 'non-aerated basins to maintain the concentration of materials in constant suspension (particles of mud in suspension).

In another variant implementation of the method shown in FIG. 2, the raw effluents 2, which have optionally undergone the pre-treatment 3, feed only the control tank 7 '. In this in this case, the non-aerated 8 'and aerated 4' basins are then supplied (circulation 16) only by the liquor leaving the control tank 7 '.

Figure 3 is an alternative implementation of the method shown in Figure 2. An additional step of biological treatment in aerobic 9 is implemented in aerated basins (referenced 9 ') between control step 7 and anaerobic biological treatment step and anoxic 8 biological treatment. Gross effluents 2, possibly from the pretreatment step 3, feed the control tank 7 'and 8 'non-aerated basins and / or 9' aerated basins of the stage additional 9. The 8 'non-aerated basins are supplied with effluents crude when nitrate concentrations are high. The ponds aerated 9 'from the additional stage 9 are fed with raw effluents 2 when the nitrate concentrations and the orthophosphates are weak. Mixtures subject to the control of bacterial growth 7 come from extra step 9 of aerobic biological treatment and / or clarification step 5 and / or thickening 6. In circulation 16, the liquor generated by the control 7 is returned to the aerated basins 9 'of the additional stage 9, and / or the non-aerated tanks 8 'depending on the nitrate concentrations and phosphorus.

The increase in recycling rates 22, 21 of non- aerated 8 'to the aerated basins 9' then aerated basins 9 'to the basin 7 'control and recycling flows 16 from the 7' control basin to the 8 ', 9' biological treatment basins are used to regulate the redox potential in the 7 'control basin but also increase the processing load within control step 7 to increase the raw effluent treatment capacity 2 of the process according to the invention represented in FIG. 3. The fluids circulate only from the control tank 7 'to biological treatment tanks 9', 8 'and from aerated basins 9 'to non-aerated basins 8', when control 7 of bacterial growth is interrupted or when the effluent flows crude 2 to be treated and muddy mixtures 15 to undergo the control step 7 are weak.

In an alternative embodiment of the above-mentioned methods according to the invention, the regulation of the redox potential is carried out by a sequenced aeration with air or pure oxygen of the control tank 7 '.

In another variant, the regulation of the redox potential is carried out by controlling the amount of muddy mixture recycled in the 7 'control tank from the 4' or 9 'aerated tanks, the non-aerated tanks 8 ', clarifiers 5' and / or thickener 6 '. Feeding the muddy mixtures into the 7 'control tank can then be controlled, for example, by varying the flow rates supply 15, 19, 21.

According to an improvement of the invention, the values of the potential redox are measured by a sensor which transmits the data corresponding to the potential values of a PLC. The machine performs an analysis and compares the values measured against the defined thresholds redox potential. Depending on the results of the analysis and to regulate the redox potential, the controller controls the power supply 10 raw effluents or muddy mixtures recycled 16, 19, 22 to the 7 'control basin, or controls the sequenced aeration of the control basin 7 '.

Figures 4 and 5 respectively represent a variant of implementation of the methods represented in FIGS. 2 and 3. In this variant the muddy mixtures from the 6 'thickener and / or clarifiers 5 'are brought upstream of the pretreatment 3, when the latter is required, and upstream of the 7 'control basin directly in the gross effluents 2 stored in the lifting pit (not shown) polluted water from treatment plant 1 or during the flow of raw effluents 2 from this pit to the pretreatment stage 3 or to the control step 7.

In another variant implementation of the method according to the invention, the 5 'clarifiers are replaced by a filtration device membrane. This is the result of this filtration which is recycled to thickener 6 ', aerated biological treatment tanks 4', 9 'and / or not aerated 8 ', the control tank 7' and / or directly in the effluents gross 2 upstream of control step 7.

For existing effluent treatment facilities, control step 7 is implemented in the buffer tank (s) of installation 1 which are placed, for example, just downstream of the raising of raw water 2 or just downstream of pretreatment 3 when these are required.

In an implementation variant of the installation 1 and for improve treatment, control step 7 may include an addition reagents such as, for example, sodium hydroxide, an oxidant or an acid. The amount of reagent used is generally less than in the prior art because it is only a complementary treatment to that of the control 7 of bacterial growth. Control step 7 can also include steam injection and / or equipment for increase the temperature of the medium and / or equipment allowing the mechanical shearing of the muddy mixture such as, for example, a high speed turbine, hydro-ejector or similar means.

In a variant implementation of the method according to the invention, the redox potential of the muddy mixture in the control 7 'is regulated around a potential value which is different from the above-mentioned potential equilibrium value (potential value close to 0 V) corresponding to the limit between the oxidizing and reducing medium. The potential redox of the muddy mixture is then regulated around a value potential which is predetermined and for example between - 150 mV and + 150 mV approximately compared to the normal hydrogen electrode. This are also measures of the redox potential and rapid and frequent alternations of the redox potential of the muddy mixture around this predetermined potential value which preserve a redox potential of the muddy mixture close to the predetermined potential value which is either negative or positive to correspond to a reducing or oxidizing medium of the mixture muddy. Typically the regulation is such that the value of the potential oxidation-reduction of the muddy mixture evolves in an interval predetermined which is approximately plus or minus 20 mV from the value of predetermined potential, the difference of 20 mV is a function of the electrode normal to hydrogen. For example, if the predetermined potential value is 110 mV, the redox potential of the muddy mixture will be regulated between 90 mV and 130 mV approximately.

When it is necessary to treat stabilized sludges whose pollutant load is low, the biological balance is obtained, as cited above, for a redox potential of the muddy mixture contained in the 7 'control tank which is regulated around a potential value predetermined redox. As previously described, this predetermined potential value is preferably equal to the value of oxidation-reduction potential (potential equal to approximately OV) but the predetermined potential value can also be a value negative (between approximately - 150 mV and 0 mV depending on the normal hydrogen electrode) or a positive value (between about 0 mV and + 150 mV depending on the normal hydrogen electrode) redox potential.

When the sludge to be treated is sludge not stabilized with a medium or high pollution load, the equilibrium organic can also be obtained for a redox potential of the muddy mixture contained in the control tank 7 'which is regulated around a predetermined redox potential value.

In another variant implementation of the method according to the invention and for non-stabilized sludges whose pollutant load is medium or high, the redox potential of the muddy mixture contained in the control basin 7 'is regulated, during the control of the bacterial growth, sometimes around a redox potential value predetermined negative (between approximately - 150 mV and 0 mV as a function of the normal hydrogen electrode) and sometimes around a positive predetermined redox potential value (included between approximately 0 mV and + 150 mV depending on the normal electrode at hydrogen). The redox potential of the muddy mixture in the control basin is then successively regulated around each of the two predetermined potential values to be maintained in a interval equal to approximately plus or minus 50 mV with respect to each value predetermined, the difference of 50 mV is expressed as a function of the electrode normal to hydrogen.

For example and for unstabilized sludges whose charge is medium or high, a potential value can be predetermined at around - 120 mV and another at +120 mV depending on the normal hydrogen electrode. When controlling growth bacterial, the redox potential of muddy mixtures in the control basin 7 'will be regulated successively and during periods of time of a fixed duration, which may for example be equal to approximately ten minutes, sometimes around the predetermined potential value and equal to around - 120 mV and sometimes around the predetermined potential value and equal to approximately + 120 mV. When the redox potential of muddy mixtures is regulated to be kept in an interval equal to approximately plus or minus 50 mV which is centered around each value of predetermined potential, the redox potential of mixtures muddy will be regulated sometimes between -70 mV and - 170 mV and sometimes between + 70 mV and + 170 mV.

The different modes of implementation represented in FIGS. 1 to 5 are chosen according to the characteristics of the pollution, such as for example: pH, temperature, TAC (full alkalimetric titer), COD (chemical oxygen demand), BOD ₅ ( biochemical oxygen demand), MeS (suspended matter), MV (volatile matter), SEH (hexane extractable substances), N / NTK, N / NO ₂ ^- , N / NO ₃ ^- , Ptotal (phosphate concentration ), Portho (orthophoshate concentration), H ₂ S / HS ^- , SO ₂ , SO ₄ ^2- ,

• de la DCO, de la DBO₅ des MeS, des MV,
• des faibles concentrations en SEH, en H₂S/HS^- , en N/NO₂ ^- , en N/NO₃ ^- et en SO₂,
• des concentrations en N/NTK et une concentration du Ptotal en équilibres par rapport aux besoins de synthèse de la biomasse.

For example, in the mode of implementation of the method according to the invention shown in FIG. 1, the pollution that can be treated includes:

• COD, BOD ₅ , MeS, MV,
• low concentrations of SEH, H ₂ S / HS ^- , N / NO ₂ ^- , N / NO ₃ ^- and SO ₂ ,
• N / NTK concentrations and a Ptotal concentration in equilibria in relation to the biomass synthesis needs.

• de la DCO, de la DBO₅, des MeS, des MV,
• des faibles concentrations en SEH, en H₂S/HS^- , en SO₂,
• des concentrations en N/NO₂ ^- , N/NO₃ ^- , N/NTK élevées,
• et une concentration du Ptotal en équilibre par rapport aux besoins de synthèse de la biomasse.

For example, in the modes of implementation of the method according to the invention shown in FIGS. 2 and 4, the pollution that can be treated includes:

• COD, BOD ₅ , MeS, MV,
• low concentrations of SEH, of H ₂ S / HS ^- , of SO ₂ ,
• high N / NO ₂ ^- , N / NO ₃ ^- , N / NTK concentrations,
• and a Ptotal concentration in equilibrium with respect to the needs for biomass synthesis.

• de la DCO, de la DBO₅, des MeS, des MV,
• des faibles concentrations en SEH, en H₂S/HS^-,
• des concentrations en N/NO₂ ^- , N/NO₃ ^- , N/NTK élevées,
• et une concentration du Ptotal élevée par rapport aux besoins de synthèse de la biomasse.

For example, in the embodiments of the method according to the invention shown in FIGS. 3 and 5, the pollution that can be treated includes:

• COD, BOD ₅ , MeS, MV,
• low concentrations of SEH, of H ₂ S / HS ^- ,
• high N / NO ₂ ^- , N / NO ₃ ^- , N / NTK concentrations,
• and a high Ptotal concentration compared to the biomass synthesis needs.

For the modes of implementation represented in FIGS. 1 to 5, when the concentrations of SEH are high a pretreatment can be implemented and when the concentrations of SO ₂ are high a pretreatment by oxidation can be implemented.

The following table makes it possible to compare the results obtained during pilot tests by a conventional treatment process (without the step of controlling bacterial growth) and a process implemented according to the invention for installations operating at low mass load. and for different types of raw effluents to be treated. Each result gives the mass of biological sludge (MeS: suspended matter) produced by a treatment installation over a given period, as a function of the BOD ₅ mass eliminated (biochemical oxygen demand) during this same determined period. These results make it possible to evaluate the efficiency of each process as a function of the mass of BOD ₅ eliminated. Dairy effluents Slaughterhouse effluents Dryness after dehydration by centrifuge Classic low load process Approximately 0.45 kg MeS / kg BOD ₅ eliminated Approximately 0.55 kg MeS / kg BOD ₅ eliminated 12 to 20% Method according to the invention under low load 0.1 to 0.2 kg MeS / kg BOD ₅ eliminated 0.15 to 0.3 kg MeS / kg BOD ₅ eliminated 15 to 25% Method according to the invention in low load and using membranes 0.03 to 0.15 kg MeS / kg BOD ₅ eliminated 0.05 to 0.15 kg MeS / kg BOD ₅ eliminated 14 to 25%

The results, obtained according to an operating procedure described below, show that the process used according to the invention is indeed more efficient than a conventional process since, depending on the different cases envisaged, the process of the invention makes it possible to reduce from 30 to more than 90 % sludge production compared to a conventional process. A immediate consequence is to be able to decrease the workshop capacity of dehydration 24 of at least 40% while preserving the quantities of effluents rough to be treated 2. Due to the higher minerality of the sludge which can be produced according to a process of the invention, the dehydration of these is significantly improved: increase of 2 to 5 dryness points (see table above).

• sur les effluents bruts 2 pour comptabiliser les matières en suspension qui pénètrent dans l'installation de traitement 1,
• sur l'eau traitée 12 pour comptabiliser les matières en suspension qui sortent de l'installation,
• sur les extractions de boues réalisées régulièrement à partir des bassins de boues, tel que notamment les bassins aérés 4', 9' et les bassins non aérés 8' de traitement biologique, afin de maintenir une concentration de boues constante et idéale dans ces bassins,
• et sur la liqueur mixte des différents bassins aérés 4', 9' ou non aérés 8' pour vérifier les concentrations de boues.

The procedure for obtaining the aforementioned results from each of the two treatment plants, one operating according to a conventional process and the other according to a process implemented according to the invention, consisted initially in carrying out daily sludge production reports over several days from average samples taken over 24 hours. These samples were taken:

• on raw effluents 2 to account for suspended solids entering the treatment facility 1,
• on treated water 12 to account for suspended matter leaving the installation,
• on sludge extraction carried out regularly from sludge basins, such as in particular the aerated 4 ', 9' basins and the non-aerated 8 'biological treatment basins, in order to maintain a constant and ideal sludge concentration in these basins,
• and on the mixed liquor from the different aerated 4 ', 9' or non-aerated 8 'tanks to check the sludge concentrations.

The mass of biological sludge generated over a determined period, for example over about six months, by a treatment installation is given by the following formula: (MeS extraction * extracted volume) + (MeS treated water) * (volume treated - extracted volume) - (raw water MeS * treated volume) = mass of sludge generated

• MeS extraction : correspond à la quantité moyenne de MeS (matières solides en suspension) par unité de volume de mélange boueux extrait à partir des bassins de traitements biologiques 4', 8', 9' contenant les boues, cette concentration est exprimée par exemple en g/l, les MeS d'extraction comprennent des particules de boue principalement organiques (45 à 90% de matière organique),
• volume extrait : correspond au volume total, en litre, de mélanges boueux extraits des bassins de traitements biologiques 4', 8', 9' qui contiennent les boues, et qui, en excès, sont évacués en dehors de l'installation de traitement durant la période déterminée,
• MeS eau traitée : correspond à la quantité moyenne de MeS par unité de volume d'eau traitée 12 (épurée) sortant de l'installation 1, cette concentration est exprimée par exemple en g/l, les MeS eau traitée comprennent des particules de boue non retenues par les clarificateurs 5' et se trouvant en suspension dans l'eau traitée,
• volume traité : correspond au volume total, en litre, d'effluents bruts 2 entrant dans l'installation d'épuration durant la période déterminée,
• volume traité - volume extrait : correspond au volume total, en litre, d'eau traité sortant de l'installation d'épuration durant la période déterminée,
• MeS eau brute : correspond à la quantité moyenne de MeS non biodégradables par unité de volume d'effluents bruts entrant dans l'installation d'épuration, cette concentration est exprimée par exemple en g/l, les MeS eau brute comprennent des particules organiques et/ou minérales en suspension dans les eaux brutes.

In this formula:

• MeS extraction: corresponds to the average amount of MeS (suspended solids) per unit volume of muddy mixture extracted from the biological treatment tanks 4 ', 8', 9 'containing the sludge, this concentration is expressed for example in g / l, the extraction MeS include mainly organic mud particles (45 to 90% organic matter),
• volume extracted: corresponds to the total volume, in liters, of muddy mixtures extracted from the biological treatment tanks 4 ', 8', 9 'which contain the sludge, and which, in excess, are evacuated outside the treatment installation during the specified period,
• MeS treated water: corresponds to the average amount of MeS per unit volume of treated water 12 (purified) leaving installation 1, this concentration is expressed for example in g / l, the MeS treated water includes mud particles not retained by the 5 'clarifiers and being suspended in the treated water,
• volume treated: corresponds to the total volume, in liters, of raw effluents 2 entering the treatment plant during the determined period,
• volume treated - volume extracted: corresponds to the total volume, in liters, of treated water leaving the treatment plant during the determined period,
• Raw water MeS: corresponds to the average quantity of non-biodegradable MeS per unit volume of raw effluent entering the treatment plant, this concentration is expressed for example in g / l, the raw water MeS includes organic particles and / or mineral suspended in raw water.

The analysis of suspended matter (MeS) consists first of all to carry out a filtration on filter paper (previously weighed) of a volume of determined sample and then in a second drying step at the oven at a temperature of around 105 ° C for 24 hours on the filter paper. The difference in mass between the filter containing the suspended matter and the blank filter calculates the concentration in g / l taking account of the determined volume of the sample.

The sludge production is then compared to the mass, expressed in g, of the BOD ₅ eliminated (biochemical oxygen demand) over the same period considered during the evaluation of the sludge mass generated by the installation. The sludge production is then expressed as a function of the mass of BOD ₅ eliminated in g MeS / g BOD ₅ (or in kg MeS / kg BOD ₅ ). To obtain maximum accuracy of the results, the determination of the mass of sludge generated and of the BOD ₅ eliminated was carried out over a period of several months, for example about six months.

Claims (31)

Method for treating polluted raw effluents (2), such as industrial and urban waste water, comprising at least one step for biological treatment (4) of raw effluents (2) leading to the production of muddy mixtures, comprising sludges organic and water, characterized in that the method also comprises a step of controlling (7) the bacterial growth of at least part of the muddy mixtures (15, 19, 21) and at least part of the raw effluents (2) to be treated. Treatment method according to claim 1, characterized in that the control step (7) is carried out in at least one receiving basin (7 ') of the part of the muddy mixtures (15, 19, 21) and of the part raw effluents (2) to be treated. Treatment method according to claim 2, characterized in that the method comprises: a step of aerobic biological treatment (4) of the raw effluents (2) in at least one aerated tank (4 ′), leading to the production of muddy mixtures, a clarification step (5) of the muddy mixtures in at least one clarifier (5 '), the muddy mixtures subjected to the step of controlling (7) the bacterial growth being removed from at least one of the two aforementioned two steps (4, 5) of biological treatment and clarification. Biological treatment method according to claim 3, characterized in that the method also comprises a step of thickening the muddy mixtures in at least one thickener (6 '), the muddy mixtures subjected to the step of controlling (7) the bacterial growth being taken from at least this thickening step (6) or one of the two aforementioned steps (4, 5) of biological treatment and clarification. Biological treatment method according to claim 4, characterized in that the method comprises an additional step of biological treatment (8) of the raw effluents (2) in at least one non-aerated basin (8 '), the muddy mixtures subjected to the step of controlling (7) the bacterial growth being taken from at least this additional step of biological treatment (8) or one of the three aforementioned steps (4, 5, 6) of biological treatment, clarification and thickening. Biological treatment method according to claim 5, characterized in that the method comprises a second step of aerobic biological treatment of the raw effluents (2) in at least one aerated tank (9 '), the muddy mixtures subjected to the control step (7) of the bacterial growth being removed, from at least this second step of aerobic biological treatment (9) or one of the four aforementioned steps (4, 5, 6, 8) of biological treatments in aerated and non-aerated basins, clarification and thickening. Biological treatment method according to one of claims 3 to 6, characterized in that the clarification step (5 ') is replaced by a membrane filtration step, the muddy mixtures subjected to the control step (7) the bacterial growth can be removed from this filtration step. Biological treatment method according to one of claims 2 to 7, characterized in that the muddy mixtures (15, 19, 21) subjected to the step of controlling (7) the bacterial growth are introduced directly into the basin of the 'control step (7) of bacterial growth. Biological treatment method according to one of claims 2 to 7, characterized in that the muddy mixtures (15, 19, 21) to be subjected to the step of controlling bacterial growth (7) are recycled upstream of the tank the step of controlling (7) the bacterial growth in the raw effluents (2). Biological treatment method according to one of claims 1 to 9, characterized in that the bacterial growth of the muddy mixture contained in a basin of the control step (7) is controlled by the measurement and regulation of the oxidation potential -reduction of this muddy mixture. Biological treatment method according to claim 10, characterized in that the redox potential of the muddy mixture is regulated around a value close to zero corresponding to the equilibrium between oxidizing medium and reducing medium in the muddy mixture. Biological treatment method according to claim 10 or 11, characterized in that the redox potential of the muddy mixture is regulated to be maintained between a negative value equal to approximately - 50mV with respect to the normal hydrogen electrode and a positive value equal to approximately + 50mV compared to the normal hydrogen electrode. Biological treatment method according to claim 10 or 11, characterized in that the redox potential of the muddy mixture is regulated to be maintained between a negative value equal to approximately - 20mV with respect to the normal hydrogen electrode and a positive value equal to approximately + 20mV compared to the normal hydrogen electrode. Biological treatment method according to claim 10, characterized in that the redox potential of the muddy mixture is regulated around a predetermined value and between - 150 mV and + 150 mV relative to the normal hydrogen electrode . Biological treatment method according to claim 14, characterized in that the redox potential of the muddy mixture is regulated to be maintained in an interval which is approximately plus or minus 50 mV relative to the predetermined potential value, the difference of 50 mV being expressed as a function of the normal hydrogen electrode. Biological treatment process according to claim 14, characterized in that the redox potential of the muddy mixture is regulated to be maintained in an interval which is approximately plus or minus 20 mV relative to the predetermined potential value, the difference of 20 mV being expressed as a function of the normal hydrogen electrode. Biological treatment method according to one of Claims 10 to 16, characterized in that the oxidation-reduction potential is measured by measuring means comprising at least one platinum or gold measuring electrode and one Ag reference electrode. / AgCl or Hg / HgCl ₂ . Biological treatment method according to claim 17, characterized in that the measurement means comprise a measurement sensor associated with an automaton which regulates the redox potential. Biological treatment method according to one of claims 10 to 18, characterized in that the regulation of the redox potential is obtained by controlling the supply of raw effluents (2) entering (10) into the basin of the 'control step (7) of bacterial growth. Biological treatment method according to one of Claims 10 to 18, characterized in that the regulation of the redox potential is obtained by regulation of the flow rate of supply of raw effluents (2) entering (10) into the the step of controlling (7) the bacterial growth. Biological treatment method according to one of claims 10 to 18, characterized in that the regulation of the redox potential is obtained by controlling the evacuation (16) of the liquor from the control basin to at least one basin aerated (4 ', 9') or at least one non-aerated basin (8 '). Biological treatment method according to one of claims 10 to 18, characterized in that the regulation of the redox potential is obtained by regulating the rate of evacuation of the liquor from the control tank (7 ') to at least an aerated pool (4 ', 9') or at least one unventilated pool (8 '). Biological treatment method according to one of claims 10 to 18, characterized in that the regulation of the redox potential is obtained by a sequenced aeration with air or with pure oxygen of the control basin (7). Biological treatment method according to one of claims 10 to 18, characterized in that the regulation of the redox potential is obtained by controlling the supply of recycled muddy mixtures in the basin of the control step (7 ) from at least one aerated tank (4 ', 9') for biological treatment, at least one non-aerated tank (8 ') for biological treatment, at least one clarifier (5') and / or at least one thickener (6 ' ). Biological treatment method according to one of claims 10 to 18, characterized in that the regulation of the redox potential is obtained by regulating the flow rate of supply of recycled muddy mixtures in the basin of the control step ( 7) from at least one aerated tank (4 ', 9') for biological treatment, at least one non-aerated tank (8 ') for biological treatment, at least one clarifier (5') and / or at least one thickener (6 '). Biological treatment method according to one of claims 1 to 25, characterized in that the control step (7) comprises the addition of reagents such as sodium hydroxide, an acid or an oxidant. Biological treatment method according to one of claims 1 to 25, characterized in that the control step (7) comprises an injection of steam. Biological treatment method according to one of claims 1 to 25, characterized in that the control step (7) comprises an increase in the temperature of the medium. Biological treatment method according to one of claims 1 to 25, characterized in that the control step (7) comprises mechanical shearing of the muddy mixture, for example, by a high speed turbine or by a hydro-ejector. Biological treatment method according to one of the preceding claims, characterized in that the circulation of the effluents between at least two stages of biological treatments (4, 8, 9) and / or between the control stage (7) and at least a biological treatment step (4, 8, 9) can be carried out in one direction or opposite. Biological treatment method according to one of the preceding claims, characterized in that the control step (7) is carried out in at least one buffer tank of a treatment installation.

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